# Symbiotic nitrogen fixation in root nodules of some legumes is caused by

$\begin{array}{1 1}(A)\;\text{Nitrosomonas}\\(B)\;\text{Rhizobium}\\(C)\;\text{Azotobacter}\\(D)\;\text{Nitrobacter}\end{array}$

Symbiotic nitrogen fixation in root nodules of some legumes is caused by rhizobium
Hence (B) is the correct answer.